Speed-responsive device



June 23, 1953 G. TQRANDOL SPEED-RESPONSIVE IDEVICE Filed June 22,'1951 42./1722512 fr 629/222 vzzao/ Patented June 23, 1953 UNITED STATES PATENT OFFICE SPEED-RESPONSIVE DEVICE Glenn T. Randol, Mountain Lake Park, Md.

Application June 22, 1951, Serial No. 232,948

20 Claims. 1 Y

The present invention relates to a speedresponsive device, and Ymore particularly to .a device .responsive to centrifugal force exerted upon a centrifugal-type vactuating mechanism in differentially counteractive relation to energizable force-transmitting means, the device being sensitive to very slight variations in such differential forces exerted kupon the actuating mechanism.

In the art of speed-responsive devices, many Vdifferent types of centrifugal-type actuating mechanisms have been proposed. However, such devices are generally sensitive only to relatively great differences in rotational speeds, .in an attempt to avoid excessive hunting or lsearching in the immediate actuating speed range. Further, the prior art devices are not actuated by speeds sufficiently low to accurately control a mechanism, such .as a vehicular power-operated change-speed gearing or a friction clutch, which must be activated and/or inactivated at relatively low vehicular speeds, preferably at or immediately prior to the vehicular stalling speed. The great need for such a speed responsiveV control means will be appreciated when the operational desirability and safety of driving speed neutralization and/or automatic clutch disengagement at approximately the stalling speed are considered, so as to utilize the compression braking power of the engine during slowing of the vehicle substantially to a stop, as at a traffic V signal or intersection. However, it will be appreciated that this specific useof a speed-responsive device of this character is only exemplary, and many other uses will suggest themselves to those skilled in the art.

It is, therefore, an important object of the present invention to provide a speed-responsive device provided with means for at least partially counter-balancing centrifugal forces exerted on the actuating mechanism thereof to provide a control which is sensitive to small differential speed changes Without excessive hunting yof the mechanism in the range of control actuation.

Another important object is the provision of governing means including centrifugal members urged in one direction by centrifugal force, in another direction by force-transmitting means, and acted upon by fluid pressure damping means to resist actuation of the members to an operated position.

Still another object is to provide a governor utilizing centrifugal force and resilient biasing means as dierentially counteractive actuating media, with counter-centrifugal movement only lil of the governor actuating mechanism being resisted -by fluid pressure damping means.

A further object is the provision of a speedresponsive mechanism including relatively angularly and laterally movable control elements having a plurality of operative positions, one of the positions being attainable under the influence of centrifugal force directly proportional to rotational speed and another of the positions being attainable under the influence of biasing means normally opposing centrifugal force-responsive movement, the biasing means actually 'and solely causing relative movement of the elements when the centrifugal forces on the members decrease below the centrifugal force-biasing means balance point.

Another object related to that next above set forth is to provide speed-responsive mechanism wherein relative lateral movement under the influence of the biasing means is modulated by and under the control of fluid pressure dashpot means.

Yet a further object of this invention resides in the provision of speed-responsive means including opposing reciprocatory pistons movable to a plurality of adjusted positions under the counteractive differential influences of centrifugal force and mechanical pressure, with movement of the pistons to one of their positions being modulated by compression dashpot means interposed therebetween.

An additional object related to that next above is to provide differential fluid pressure dashpot means having vent valve means effective to control dashpot pressures so that effective dashpot action occurs only upon movement of the reciprocatory pistons in a single direction.

A more specific object of the present invention is the provision of speed-response means wherein centrifugal-force responsive movement of a plurality of centrifugal members is utilized to operatively energize pre-loaded compression elements which are effective, upon attainment of minimum rotational speed and resultant minimum centrifugal force, to solely cause countercentrifugal movement of the centrifugal members, and means responsive only to such countercentrifugal movement to damp such movement to thereby enable further reduction of the rotational speed at which actual control movement of said members occurs.

Yet another object is to provide a speed-responsive device having a pair of relatively movable contact elements, the elements being relatively rotatable about a common axis and also relatively movable in lateral alignment into and out of engagement.

A further object related to that next above is the provision of means energized as a consequence of relative rotation. of the elements to resist movement of the contact elements both into and from engagement.

Other and further important objects of this invention will be apparent from the disclosures in the specification and the accompanying drawings.

This invention (in a preferred form) is illustrated in the drawings and hereinafter more fully described.

In the drawings:

Figure l is a plan elevational view of a speedresponsive device of the present invention;

Figure 2 is a vertical sectional view taken along the plane II-II of Figure l, illustrating the control elements of the device in an operated (closed) condition and the dashpot means under atmospheric conditions;

Figure 3 is a transverse sectional view taken along the plane IlI--III of Figure 2 further illustrating details of the contact elements when the same are positioned as shown in Figure 2.

Figure 4 is a fragmentary sectional view similar to Figure 2 illustrating the control elements in a different operated (open) condition and the dashpot means actuated (open) to facilitate relative centrifugal movement of the control elements; and

Figure 5 is a fragmentary vertical sectional view taken along the planes V-V of Figure 3 illustrating further details of the movable contact end structure.

Referring to the drawings:

In Figures l-5, inclusive, reference numeral Ii) refers generally to a speed-responsive device of the present invention particularly constructed and arranged to be actuated from one operative position to another by minimum speed, or other actuating force, variations.

The device includes an exterior casing provided with an upper, generally cylindrical casing section l! defining an open-topped inner chamber I2 overlying a lower mounting block portion I3 having an exteriorly threaded shank I4 provided with an axial bore I5. The bore it terminates at its upper end in a radially enlarged shoulder |'I defining an open-topped counterbore I8 in full communication with the chamber I2. The casing shank., portion |4 is threadedly received by a matingly threaded aperture I9 formed in a support structure 2G, which f:

may conveniently be a transmission housing through which a transmission output or propeller shaft 2| passes. The output shaft 2|, or other source of control speed, carries for rotation therewith a worm or similar toothed member 22, which member 22 meshes with a Worm gear or other matingly toothed member 23. The member 23 is pinned or otherwise co-rotatably secured as at 24, to a driven shaft 26 which serves to actuate the control elements of the device, as will be hereinafter described in greater detail.

The open-topped chamber I2 of the casing is closed by an insulated cap 2l' which is circular in configuration and which carries an integrally formed, depending annular ange 28 snugly ttable into the recessed casing II to provide a snug dust-tight closure for the chamber I2. The cap 21 is detachably secured to the casing by suitable means, as by cap screws 29. The

cap inner surface carries an inwardly'projecting dished contact element 30 which is fixedly secured to the cap 2l by a center rivet-head 3| forming a terminal end of a contact post 32 projecting upwardly through the cap. The contact post receives contact washers 33 thereon exteriorly of the casing for confining therebetween a contact bight 34 carried by a lead wire 36. The washers are urged toward one another and into good electrical contact with the bight 34 by a nut 31 threadedly receivedy by the free end of the post 32.

'Ihe dished contact element 3|) is retained against rotation by ears 38 struck upwardly therefrom for extension into the insulated cap 2l. The depending peripheral flange 39 of the element 30 projects into the chamber I2 and the exposed exterior surface 40 of the flange 3S provides a continuous annular contact surface Which cooperates with the centrifugal forceresponse elements of the'device as will later become apparent.

The shaft 25 is journalled for rotation within` formed integrally therewith or pinned thereto for co-rotation, and the boss 43 forms a part of a rotor indicated generally at 44. The rotor 44 is generally cylindrical in shape (Figure 3) and is provided with oppositely directed, radially extending embossments 46 having upper web portions 4l' joining the embossments 46 to the rotor proper.

The diametrically opposed embossments 46 are v joined by'a Asingle continuous cross-bore 48 extending diametrically through the rotor and axially through the embossments. The embossments are each provided with slots 49 communicating with the cross-bore 48 at the outer radial ends of the cross-bore, the slots 49 thus extending axially of the rotor and normal to the axis of the cross-bore 48, and the slots actually being formed in the upper Web portions 47 hereinbefore described.

The bosses 4t are each adapted to receive, Within the respective cross-bore portions thereof, a movable contact element 5|) which is reciprocablejaxially within the cross-bore 48, the reciprocation of the elements 5t being radial withv More particularly, the

respect to the rotor 44. elements 50 each comprise a piston portion 5| lsnugly received bythe cross-bore and a projecting` contact armportion 52 adapted to project radially of the piston portion and through the slots 49 axially of Athe rotor into proximity with the fixed contact flange 39.

The piston portions 5| of the movable elements 5I] are provided with axially extending recesses 53 having closed inner ends 54 against which are bottomed compression spiral springs 5E. The outer ends of the springs 56 are bottomed against circular Washers 51 retained in shallow counterbores 58 formed in the outer en'd of the bosses 46 (Figure 2). The Washers 51 are retained in the counter-bores 5b by lock rings 59, and the Washers are provided with inwardly projecting central nipples 68 so as to positively guide the springs 56 for compressive and expansive movements.l

The cross-bore 43 communicates with la second bore 6| extending axially of the rotor 44 inwardly from the free upper surface thereof to intersect the cross-bore 48 and to project therebeyond, as at 62. The outer or upper end of thev bore 6l is countersunk to provide an linner radial shoulder 63 and is again countersunk to provide an outer, radially larger shoulder B4 against which is press-fitted or otherwise secured a valve seat insert 66 having an inner, inwardly divergent, frusto-conical valve seating face 61 surrounding a central air escape port 68.

The valve seating face 61 is adapted for co- ;action with a peripheral correspondingly frustoconical valve face 69 carried by a check-valve 10 having a stem 'H depending axially into the axially aligned bores 6I and 62. The valve stem 1| is surrounded by a spiral compression spring 72 bottomed against a shoulder 13 defined by the inner end of the bore 62 and a smaller axially aligned bore 14 extending therebeyond. The free vlower terminal end of the valve stemll is projected into the bore 14 for guiding the checkvalve face 69 into proper sea-ting relationship with its xed cooperating face 51. A plurality of semi-circular air utese'l are formed in the surface of the bore 14, and of such length as to maintain the lower end of said bore vented to the cross-bore 48 whereby compression or suction action on the lower end of the valve stem 'Il is prevented during check-valve actuation. Thus, the stem is guided by the bore 'H for axial movement to carry the valve head 'I0 into and out of engagement with the valve seat 61 either under the influence of or against the compression of the spring 12.

The valve and the stem 1I thereof are provided with an open-ended axially extending airbleed passage 8i communicating at its inner end with a radial passage 82 communicating with the ,interior of the bores 48 and 6| in the area of junction thereof. The passages 8| and 82 thus provide restricted means for air to escape from the bores without passing through the valve opening 68. The interior of the casing H is vented to the atmosphere through the opening 83 therein- It will be seen from Figures 2 and 4 that the contact arm portions 52 of the elements 50 terminate in inwardly directed arcuate contact faces 80, and these faces are adapted to cooperate with the exterior peripheral contact surface 40 of the contact member 39 upon reciprocation of the pistons 50 by differential counteractions of centrifugal force and pressure of the springs 56.

Operation,

To better comprehend the operation of the present invention, let it be assumed that the rotary shaft 2| is the propeller shaft or output shaft of an automotive transmission, so that the rotational speed of the shaft is directly proportional to the road speed of the vehicle. Further let it be assumed that the conductor 35 forms a part of a control circuit for an automotive clutch which is automatically engage-able and disengageable in response to the flow of electric current through the conductor.

When the switch contact elements are closed, as when contact faces B0 of the arms 52 contact the peripheral face 40 of the element 30, current flow through the conductor is grounded through the entire assembly l0, and direct current iiow through the assumed control circuit can occur. When the contact elements are open, as in Figure 4, no current ow `can occur. Thus, it will be appreciated that the'present invention provides means for controlling current flow through the conductor 3B and an assumed control circuit associated therewith. l

When the shaft 2| is rotated at a speedsufcient to generate a substantial centrifugal force suflicient to throw the elements 50 radially outwardly against the compression springs 5B, the pistons will assume the radial positions illustrated in Figure 4 and the contact faces 40 and of the elements 30 and 50, respectively, will be separated. Thus no current iiow through the contact elements is possible. The washers 51 will serve to limit outward movement of the elements 50 and the outward centrifugal force-responsive movement will serve to compress the springs 56.

As the rotative speed of the shaft 2l decreases, the ratio of the spring compressive force to the outward centrifugal force will increase until such time as the forces become balanced. After this counterbalancing action occurs, further decrease in speed produces a differential counteraction between the centrifugal and spring forces whereby the elements 50 will be moved inwardly until the springs 55 force the contacts closed. Obviously, the exact moment of contact element contact may be primarily controlled by the compressive strength of the springs 56.

The pistons 5| fit quite snugly in the bore1'48, and the pistons in combination with the valve 10 provide a dashpot means for ymodulating element closure in order that the same may be more precisely controlled. More specifically, the dashpot means functions to control the rate of piston inward movement to nal element-engaged position, without interfering with radially outward, contact-breaking piston movement.

As the pistons move radially outwardly, a vacuurn is created n the bores 48 and 6l by virtue of the enlarged area between the pistons. This vacuum draws the valve 1U open against the action of the spring 12 before the vacuum becomes suiiicient to substantially interfere with outward piston movement. Thus, there is no interference of differential pressure with outward piston movement, since air at atmospheric pressure is introduced into the potential vacuum area by the valve opening movement. This. conditionV of venting the bores 48 and 5| to atmospheric conditions is speciiically shown in Figure 4.

On the other hand, as the centrifugal forces upon the elements lessen and the spring-centrifugal force ratio increases, the pistons 5` are forced into the damping chamber deiined by the bores 48 and 5l. Thus, the size of the chamber is decreased and air therein, originally under atmospheric pressure, is placed under compressive greater-than-atmospheric pressures, since the valve il! is closed by the spring 'l2 as soon as the air pressures in the chamber and the casing il are equalized. This superatmospheric air pressure will resist further inward movement of the pistons 5I, and, although a portion of the air will be bled oiT through the bleed passages 8l and 82,-these passages are restricted so that the air pressure in the chamber is only slowly lessened.

The resulting substantial impedance of inward piston movement will damp final relative contacting movement of the faces or surfaces 40 and 80, so that closing movement of the elements will be substantially delayed so as to occur only after the speed of the shaft 2| has dropped well below that speed necessary to generate sufficient centrifugal force for resisting the spring contactclosing force. In other words, the uid pressure fdamping 'structure 'provides `means for v'delaying switchelosingl'movement -until a substantially non-rotational condition Vof-thefshaft V2| exists, `whilev rapid Y centrifugal force-responsive switch "opening movement is possible.

' In "addition tothe `close control of contact- `closing movement at extremely low rotational 4speedsnal closing movement occurs as a result Aof vthe sole effort of the springs 56 as modulated 'by" the fluid pressure damping means. ffirial,` sharp closing movement of the contact ele- Thus, a

:ments isl obtained at a predetermined slow rotaytional speed. The inward closing movement of Athepistons is substantially entirely radial, and

electrica-l arcing across contacts is thus prevented.l `A minimum of relative rotational movement between the contacting surfaces 40 and 8G occurs,

Lsethat it is-practical for the nrst time to utilize frelatively rotatable electrical contact surfaces in a speed-responsive device with avnegligible .wear` factor.

It; 'will be understood that modifications and variations may be effected without departing fromthe scopecf thev novel concepts of the 'presenti invention as defined in the claims appended I claim as my invention:

1; yA speed-responsive device comprising a shaft adapted to be rotated at varying speeds, a rotor 'rotatable withV said shaft and having a radial -Vcross-bore therein, a fixed contact element located 'in spaced relation to said rotor, a piston movable .in said cross-bore in response to rotational speeds ofisaid rotor, 4said piston being movable radially outwardly of said rotor by centrifugal forces gen erated upon rotor rotation, a contact element movable withsaidpiston into and out of contact 'Withsaid fixed element, and spring means urging ,said piston radially inwardly in opposition to said centrifugal force.

2; Afspeed-responsive device comprising a shaft ladapted to be rotated at varying speeds, a rotor #uponrotorfrotation, contact arms carried by said pistons and projecting therebeyond for movevment into and out of contact with said fixed element', and lspring means yacting directly upon -saidipistons tobias the same radially inwardly-.in

opposition vtosaid -centrifugal force.

1' 3. Arspeed-responsive device comprising aro- :tary shaft-adapted. to be driven at varying speeds,

elements disposed in ya common plane on said vshaft for movement radially outwardly therefrom in' response to centrifugal forces developed upon rotation of said shaft, means operative in the plane 'of movement of said elements for opposing radially outward movement thereof and effective to force said elements radially inwardly upon a decrease in centrifugal force, uid pressure damping means in direct fluid communication with said Aelements for modulating inward radial movement of said elements under-the force of '.said'first named means, and means for driving said rotary shaft at varying speeds.

"4.- Aspeed-responsive device comprising a' rotary shaft adapted to be driven at varying speeds, diametrically opposed elements disposed in a common plane on said shaft for movement radially' outwardly therefrom in response to cenfi 'l trifugal' forces developed upon rotation-'of said shaft,- means operative in the planeofmovement of ysaid elements for Aopposing radially outward movement thereof and effective to force saidelements radially inwardly upon a decrease in centrifugal force, and fluid `pressure damping means interposed between said elements for modulating inward movement of said elements under -t-he force of'- said first named means, said fluid 'pressure Ydamping means including a fluid pressure chamber of varying volumeV with the volume thereof decreasing 'l assaid-elements are forced radially inwardly,` and `restricted bleeding passages providing a sole exit for fluid under --pressure in said chamber.

5. A speed-responsive device comprising a rotary shaft adapted to be driven atvaryin-g speeds, elements on said shaft for movement radially outwardly-'therefrom in response to centrifugal forces developed upon rotation of said shaft, means operative in the plane of Vmovementof said elements for opposing radially outward movement thereof and effective to `force said elements radiallyinwardly upon a decrease in centrifugal force, and fluid pressure damping meansfor modulating inward movement'of said elements yunder the force of said first-named means, saiduid pressure damping means including a'fluid pressure chamber of varying volume with the volume thereof decreasing as said elements lare forced radially inwardly, valve means controlling venting of said chambertothe atmosphere and operated-to a closed position when atmospheric-or superatmospheric conditions existin said chamber, and a bypass exit of relatively small capacity for accommodating the escape of iiuid under pressure fromsaid chamber-despite the closed position of said valve means.

6. A speed-responsive device comprising a rotary shaft adapted to be driven atvaryingspeeds,

a rotor rotatable with said shaft, a xedcontact element concentric with but axially spaced from vsaid rotor, a plurality of movablecontact elements radicallyl disposed in a single plane about the axis of said rotor and normally bridging the-axial space between said rotor and said xed element,

said movable elements being reciproca-ble radially of the axis of said rotor in response to centrifugal forces generated upon rotation thereof, and means "effective to hinder movement ofv said movable elements in both radial directions to thereby vary the rate of speed-responsive movement thereof.

7. A speed-responsive device comprising a-*rotary shaft adapted for rotation at varying speeds, a rotor rotatable with said shaft and having a cross-bore extending radially therethrough, a 'plurality of reciprocatory pistons radially sli'dable iniopposing endsof said cross-bore anddening a fluid-tight air-chamber therebetween, said' pistons beingmoved radially outwardlyby centrifugal forces developed upon rotation of said shaft at speeds equal to or above a predetermined value, means urging said pistons radially inwardlywhen said shaft rotates at speeds equal to or less than a second predetermined value, valve means operable to an lopen position when said pistons are moved outwardly and operable to a closed position thereafter so that atmospheric pressureis maintained in said chamber, and means by-passing said valve means and affording only restricted bleeding of air from said chamber during inward movement of said pistons tov modulate the rateof suchinward movement. n

8. A speed-responsive device comprising apluralityof relatively movable contact elements,

means for causing longitudinal reciprocatory movement of one of said elements while imparting rotarymovement thereto about an axis normal to'the direction of reciproca-tory movement, nuid pressure damping means comprising at least one of said contact elements and energized as a result of reciprocatory movement of said one of said contact elements to impede relative movement of said contact elements, valve means including a movable element for controlling energization of said last-named means, and means for imparting rotary movement to said elements.

9. A speed-responsive means comprising a plurality of relatively movable contact elements, one of which is movable longitudinally into and out of contact with lthe other, means for rotating said one element about an axis displaced from the one element itself so as to cause said longitudinal movement, and a fluid pressure chamber, the volume of which varies in directrelation to movement of said on-e element with movement of said one element toward said other element generating super-atmospheric pressures therein to modulate further movement of said one element.

10. In a speed-responsive device, a plurality of relatively movable contact elements, a fixed contact, means for relatively moving said elements in a common plane into and out of engagement with said fixed contact, means Vfor rotating said elements relatively about a common axis normal to the aforesaid common plane thereof, and means energized as a consequence of relative rotation for resisting relative movement of said elements both from and into engagement with the said fixed contact. e

11. In a speed-responsive device having a plurality of radially movable contact elements responsive to centrifugal forces exerted thereon, means for damping radial movement of said elements by fluid pressure including a fluid-tight compartment therebetween, pistons formed integrally with said elements for movement therewith to vary the volume of said compartment, and means controlling the ingress and the egress of atmospheric air and super-atmospheric air to and from said compartment respectively.

12. In a speed-responsive device having a plurality of radially movable Contact elements responsive to centrifugal forces exerted thereon, spring means acting on said elements to urge the same to an adjusted radial position, and means for damping radial movement of said elements by fluid pressure including a fluid-tight compartment therebetween, pistons formed integrally with said elements for movement therewith to vary the volume of said compartment, and separately effective atmospheric vent ports of different sizes to promote rapid ingress and relatively slow egress of air.

13. In a speed-responsive device having a plurallty of contact elements movable radially by differential counteractions of centrifugal and compressive spring forces, means for modulating radially inward element movement including means defining an air chamber between said elements, means movable radially with said elements into and out of said chamber to vary the volume thereof, and a restricted air escape port for slowly bleeding air from said chamber as the same is compressed therein by movement of said lastmentioned means thereinto.

14. In a speed-responsive device, a rotor adapted to :be rotated about a longitudinal axis at varying rotational speeds and having a radially extending open-ended bore therethrough, said rotor also having an axial recess communicating with said bore, a plurality of opposed pistons projecting into the open ends of said bore for radially outward movement therein due to centrifugal forces generated upon rotation of said rotor, spring means acting on said pistons to oppose radially outward movement thereof and being operatively energized during such movement to urge said pistons radially Vinwardly against centrifugal force, and valve means modulating radially inward piston movement including a valve located in said axial recess and controlling venting of said bore to the atmosphere and a restricted bypass incorporated in said valve to afford a Sole outlet for air from said bore upon radially inward movement of said pistons. a

15. In a speed-responsive device, radially movable control elements actuated radially outwardly by centrifugal force, spring means operatively energized by outward movement of said elements for urging the same radially inwardly, fluid pressure modulating means in direct fluid communication with said elements and concentrically disposed with respect to the common axis about which said control elements actuate and effective for differentially accommodating outward movement of said elements and opposing inward movement vof said elements to vary the rate of radially inward movement thereof, and means for generating centrifugal force on said elements.

16. In a speed-responsive device, a centrally located xed contact element, a plurality of movable contact elements adapted for Contact with said fixed contact and disposed for rotation at varying speeds about an axis common to said fixed element and said movable elements, means accommodating movement of said movable elements in a common plane radial to said axis and in accordance with centrifugal forces generated upon rotation yof said movable elements, means biasing said movable elements radially inwardly toward said fixed element at rotational speeds equal to or less than a predetermined value, and means causing an appreciable time-lag in radially inward movement of said movable elements after speeds less than said predetermined value have been obtained, so that actual closing contact of said elements occurs at speed less than said predetermined value.

17. In combination with a speed-responsive device having a rotatable centrifugal element movable inwardly and outwardly with respect to its axis of rotation as a function of its speed of rotation; means biasing said element inwardly when rotating at speeds equal to or less than a predetermined value; a duid-pressure dash pot including said element operably energizable during outward movement of said element for exerting a differential damping force directly on said element to substantially retard inward movement of said element; Valve means including a movable element automatically operable for controlling operative energization of said duid-pressure dash pot; and means for rotataing said element at different speeds.

18. In combination with a speed-responsive device having rotatable elements movable toward and away from their axis of rotation as a function of their speed of rotation, means biasing said movable elements toward their axis of rotation when rotating at speeds less than a predetermined speed, a fluid-pressure device for exerting a differential damp-ing force on said elements to substantially impede only movement of said elements toward said axis, said device including `a variable 1 l volume air chamber, a single-acting'vent valve associated with said chamber to vent the same to the atmosphere when said elements move from said axis, and a restricted by-pass yfor solely venting said chamber to the atmosphere upon movement of said elements toward said axis.

19. In combination with a speed-responsive device having rotatable elements movable toward and away from their axis of rotation as a function of their speed of rotation, means biasing said movable elements toward their axis of rotation when rotating at speeds less than a predetermined speed, a fluid-pressure device for exerting a differential damping force on said elements to substantially impede only movement of said elements toward said axis, said device including an air chamber, a reciprocable piston movable with each of said elements and enterable into said chamber upon movement of said elements toward said axis to substantially reduce the volume of said chamber, a single-acting vent valve associated with said chamber to vent the same to the atmosphere when said elements move from said axis,land a restricted by-pass for solely venting said chamber to the atmosphere upon movement of said elements toward said axis.

20. In a speed-responsive device; a xed oon- -tact element; a plurality of movable contact elements coaxially disposed in radially overlapping relation with respect to said xed contact element, said movable `elements being adapted for relative rotation and consequentrelative radial movement with respect to said xed element upon rotation at varying speeds; fluid-pressure dashpot means associated with said movable elements and operatively energizable by relative movement of said movable elements in one direotiomto oppose relative movement of said last-named elements in a different direction; valve means in. cluding a movable element for controlling energization lof said dashpot means; pre-energized spring means additionally energized in response to relative movement of said movable elements in said one direction, to oppose relative movement of said last-named elements in the last-named direction; and means for rotating said movable elements at varying speeds. Y

GLENN T. RANDOL.

References Cited in the le of vthis patent UNITED STATES PATENTS Number FOREIGN PATENTS Number Country Date France Oct. 10, 1921 

